Ez Flo Impact Flow Scale graduates from weighing Baghouse Dust out of an Auger to RAS out of a Feeder Bin. RAS (Recycled Asphalt Shingles) and RAP over the same Belt Scale; the biggest problem is that the control system has no idea what is coming out of either bin all the time. Bins do bridge, feed throats do get clogged, RAS Density can change. After the Feeder Scale was certified accurate, a test was conducted to monitor the consistency of bin output at a given speed. The Feeder Scale reports normal changes of flow of plus and minus 1.5 TPH. This indicates that the assumption the industry is depending upon for the accuracy required for an ingredient as important as RAS is not an adequately accurate method to control RAS. Clarence Richard Co. manufactures continuous weigh scales (EZ Flo) for difficult materials that are being added to the mix process. Mix Producers are adding Recycled Asphalt Shingles (RAS) to their mix and are probably having a problem accurately metering RAS into the process. This is a problem because the existing equipment today at the plant does not accurately measure the RAS Flow Rate. Adding an EZ Flo Belt Feeder Scale can enable your control system to perform as specified. 1
There are few reasons that the existing equipment is not adequate. 1) RAS carries a lot of oil in them. When accuracy is off, the oil content is affected by the error 3 to 4 times when compared to the oil content of RAP. 2) Sometimes producers us a Double Bin Rap System with Rap in one bin and Shingles in another while weighing the combination of both over one Rap Scale. It s anyone s guess how much is coming out of either bin at any given time ) The Rap Conveyor was built for heavier TPH flow rates of RAP productions. The Rap Scale System (conveyor included) was not built to accurately weigh material at such a low flow rate. 3) There is no way to know all the time if the feed throat is clogging up, or density is changing. 4) The Rap Conveyor was built for heavier TPH flow rates of RAP productions. The Rap Scale System (conveyor included) was not built to accurately weigh material at such a low flow rate. Some belt scale manufacturers refuse to weigh light loaded products such as RAS for Belt Scale applications. The Feeder Scale can measure more accurately at low flows than the belt scales are capable of doing. 2
The scale is normally being monitored by the plant computer. Plant computers are programmed to either compensate for the oil when the Rap Scale deviates from Set point or to increase or decrease both Feeder Bin Speeds. Either way, one scale is not enough. Now, the mix producer has the option of weighing the RAS and controlling that bin or the oil being added to the mix. The same RAS Rate Signal being used to control for the RAS and can be subtracted from the RAP Belt Scale (now weighing both RAS and RAP) indicating what the actual RAP TPH Flow Rate is. Now, the plant computer can use RAP deviation information to: a) adjust the oil being added to mix or b) the RAP Feeder Speed. Up until last month, when Ez Flo was given the order by Henningsen Construction to develop and build a scale to do an adequate job, such equipment was not available. The Ez Flo Belt Feeder Scale is built specifically to retrofit to most any existing RAP Bin to weigh material as it is falling from the feeder to the collector below. 3
RAS (Recycled Asphalt Shingles) Continuous Weigh Scales for Drum Mix Plants and Batch Plants. Ez Flo Continuous Weigh Scales were first developed in 2003 to replace the weigh depletion pod without the high costs to own and operate and the mix quality problem commonly associated with weigh pods. Later, Omann Bros, St. Michael, MN required a scale to weigh the material as it fell from the discharge end of a constant speed conveyor feeding a slinger into a batch plant pug mil. The same concept used in 2003 for Austin Bridge and Road to weigh dust, mineral filler and fiber is being used with some adjustments in the New Belt Feeder Scale. The challenges were to: 1) capture, accurately weigh and release the material in such a short drop between the Belt Feeder Discharge and the Collector Belt Feeder Scale 2) in a means that RAS would not build up on plate and 3) not be affected by the wind. 4
The Flow Scale impact plate is mounted 6 away from the end of the Belt Feeder Head Pulley. Picture Left illustrates the material flowing out the bin and under the NO Flow Switch and falling over the head pulley to the Impact Plate below. The Feeder Gate Level is normally set at 4 to keep material chunks out of the mix. The Flow Scale easily recognizes bridging problems even in instance the NO Flow Switch does not recognize that a chunk is impeding flow on one extreme side of the feed throat or the other. Sometimes feed throats build up with material; the flow scale recognizes that and reports the actual flow to the control system. Picture Right illustrates the RAS falling from the Belt Feeder to the Impact Plate below and then to the Collector Belt below the Impact Plate. 5
The Ez Flo Scale Calculator is shown with the documented results of what happenned after the first ever installation of the Ez Flo Feeder Scale. April 15/2012: Test 1 and 2 was used to get the Flow Scale to read in the ball park. Tests 3, 4 and 5 were used to dial in the flow scale at near 15 TPH. To check for linearity; the speed of Test 7 was increased from 22% to 31% speed resulting in a near 20 TPH Flow Rate and then lowered to about 18% speed which resulted in near 12 TPH flow rate. The significance of the last few tests is that the accuracy held at all three ranges (12 15 20 TPH) indicate that the Ez Flo Feeder Belt Scale was accurately repeatable and just as important accurately linear. And important as well, after each and every test, the Flow Scale returned to a very near zero. 6
How it Works.. EZ-Flo Continuous Weigh Belt Feeder Scale The flow scale works much like a belt scale except it does not need a tachometer since it knows the speed of the material passing through it is constant (gravity). Do not confuse the Flow Scale with meters. Meters read volumetrically. Meters do not have load cells and meters do not weigh gravimetrically. Meters read air much like cold feed bin, vane feeder or a positive displacement asphalt meter. They can make a closed loop control system an open lop since it does not actually know the flow and therefore can only assume it. Just like all he typical EZ-Flo Scales as well as RAP and Virgin Belt Scales; the Feeder Scale is sensitive to air flows such as wind. The Feeder Scales are shipped as an easy to assemble type Erector Set for ease of shipping and ease of installation. The space, the Feeder Scale is placed in, is often very small and impossible to place something of such great volume into. Therefore, the owner has the option to assemble most of or part of the flow scale inside or outside of the confined area. The area is so confining, that the frame and scale inner workings are shipped without the enclosure to keep the wind out. As part of the system, the owner agrees to protect the Impact Plate from air flows by draping some material around the flow scale area. Draping a material around the scale can usually seal up the Scale area adequately. Old conveyor belting works very well as enclosure material. The Flow Scale reads the Rate of Material Flow as it impacts the front face of the Impact Plate. The two different readings displayed on the Integrator indicates information common to your automobile instrument panel. The Rate reading (TPH is much like the Speedometer MPH) indicates how fast material is passing through the flow scale and produces an output signal very useful for blending materials. The Totalizer reading (Tons or other engineering units is much like the Odometer) is used for calibrating the scale, cross checking accuracy, inventory control and produces a signal capable of batching product. How it Works... The plate is suspended from a hinge. Material flows off the end of the Feeder Belt impacting the Plate. The Plate is forced away from the flow against the Load Cell Rod. The force is measured by a Load Cell and converted into a Rate Signal. The Flow Scale discharges the material as soon as it receives the material. Patent 7007557 and Patent Pending www.ez-flo.us 952-939-6000 clarence@clarencerichard.com 7